Wireless communication systems with reduced power consumption are known (see Patent Documents 1 and 2). The wireless communication system of Patent Document 1 includes a host, a router and an end device.
The router relays wireless communications between the host and end device. Each of the router and end device has a sleep mode and an active mode. In sleep mode, a communication function based on Zigbee (Registered Trademark) is off; in active mode, the communication function based on Zigbee is on.
When the end device in sleep mode detects a temperature abnormality by means of a temperature sensor connected with it, it transmits a WAKE-UP signal to the router. When the router receives the WAKE-UP signal from the end device, it transitions from sleep mode to active mode to relay wireless communications between the end device and host.
The router has wireless circuitry for normal wireless communications, where only two circuits, i.e. the frequency conversion circuit and radio field intensity detection circuit, are active in sleep mode to detect WAKE-UP signals.
The wireless communication system of Patent Document 2 includes an in-band communication device and an out-of-band communication device. The out-of-band communication device is connected to the in-band communication device. The out-of-band communication device receives out-of-band wireless communication information to activate the in-band communication device, thereby causing the in-band communication device to transition from sleep mode to active mode.
Patent Document 1: JP 2007-104174 A
Patent Document 2: JP 2007-526655 A